When a headlight stops working, it is tempting to order a new unit straight away. But headlights are expensive, and the fault is often somewhere else. Working through the likely causes in order can save money, and knowing what to check before buying makes sure a replacement unit fits and works first time.
Start with the simple checks
Before suspecting anything expensive, check the basics:
- Is it one light or both? If both have failed together, a fuse, relay, switch or control unit is more likely than two bulbs.
- Is it dipped beam, main beam or sidelight? Many lights use separate bulbs or circuits for each.
- Is there a warning on the dashboard? Many cars report bulb failures, and some log a fault code.
- Check the fuse for that light in the fuse box, using the diagram in the handbook.
Step 1: The bulb
On halogen headlights, a failed bulb is by far the most common fault. Look at the filament for a break or a dark, blackened glass. Replace bulbs in pairs, so both sides give the same light colour and brightness. Don't touch the glass of a halogen bulb with bare fingers, as oils from your skin can shorten its life.
Step 2: Xenon bulbs and ballasts
Xenon, or HID, headlights use a gas-discharge bulb and an igniter and ballast that produce a very high starting voltage. Typical symptoms are:
- A light that flickers, turns pink or purple, or cuts out after a few minutes: often an ageing bulb
- A light that won't strike at all: could be the bulb, the igniter or the ballast
Swapping the bulbs from side to side, with the lights off and the car switched off, is a common way to narrow it down. If the fault moves with the bulb, the bulb is at fault. If it stays on the same side, suspect the ballast, igniter or wiring. Xenon systems run at dangerous voltages, so take care and follow the manufacturer's procedure.
Step 3: LED headlights and modules
Many newer cars use LED headlights. The LEDs are usually built into the headlight or into a replaceable module, along with control electronics. When an LED headlight fails, the cause is often a driver module, a power module or the unit itself. Some modules can be bought separately, while some faults mean replacing the whole headlight. The manufacturer's parts diagrams show which parts are available on their own. Our guide to exploded parts diagrams explains how to read them.
Step 4: Wiring and connectors
Corroded or loose connectors behind the headlight are a common cause of intermittent faults. Look for green corrosion, melted plastic or broken locking tabs. Water in a headlight can also damage the bulb holder and electronics, so check the seals and the rear cover.
When the whole unit needs replacing
A new headlight is the right answer when the lens is cracked, the housing or mounting tabs are broken, water keeps getting in, or an integrated LED part has failed. Before ordering, check these points carefully:
- Side: left and right are described from the driver's seat. In the UK the driver's side is the right-hand side.
- Market: UK cars need right-hand-drive headlights that dip to the left. Units made for left-hand-drive countries dip the wrong way.
- Light type: halogen, xenon and LED units are not interchangeable without other changes.
- Facelift: headlights often change shape at a mid-life update, even if the car looks almost the same.
- Extra features: cornering lights, adaptive lights and automatic levelling need the matching unit and wiring.
Getting the right part number
Headlights are one of the best examples of why the part number matters. On Volkswagen Group cars the headlight type is linked to option codes recorded against the VIN. Hyundai, Kia and Ford use different numbers for halogen and LED units and for pre- and post-facelift cars. Our guides to using your VIN and reading VW Group part numbers will help you confirm the right one. If your old headlight is still on the car, the part number is usually printed on a label on the housing.
Shop genuine headlights
A genuine headlight gives the correct beam pattern, fits the car's mountings and seals properly against water. Browse our Volkswagen, Ford, Hyundai and Kia parts, or search by part number. All our parts are new and genuine.